The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Compressors may be used in a wide variety of industrial and residential applications to circulate refrigerant within a refrigeration, heat pump, HVAC, or chiller system (generically “refrigeration systems”) to provide a desired heating or cooling effect. In any of the foregoing applications, the compressor should provide consistent and efficient operation to insure that the particular application (i.e., refrigeration, heat pump, HVAC, or chiller system) functions properly. A variable speed compressor may be used to vary compressor capacity according to refrigeration system load.
Compressors may include crankcases to house moving parts of the compressor, such as a crankshaft. Crankcases may further include lubricant sumps, such as an oil reservoir. The lubricant sumps include lubricants that lubricate the moving parts of compressors. Lubrication of the compressors may improve performance and/or prevent damage.
Lubricants in the crankcases may cool to low temperatures when the compressor is not running. For example, the crankcases may cool due to a low outdoor ambient temperature. Additionally, lubricants may cool due to liquid refrigerant that returns to the compressor during the running cycle, otherwise known as “liquid flood-back.”
Lubricant properties may change at low temperatures. More specifically, lubricants may become more viscous (i.e., thicker) at low temperatures. Thus, starting a compressor with a low temperature crankcase (i.e., cold lubricant), otherwise known as a “cold start,” may result in damage to the compressor and/or decreased performance due to insufficient lubrication. In addition, liquid refrigerant may enter the compressor when the compressor is on or off. The liquid refrigerant may also change properties of the lubricant. Therefore, compressors may include heating elements to heat the crankcase (and in turn the refrigerant and lubricant) in order to avoid problems related to “cold starting.”